This invention relates to a circuit arrangement for igniting a lamp, comprising input terminals for connection to a power supply source,
a first capacitive element, PA1 a first circuit component coupled to the first capacitive element and to the input terminals for generating a charging current from a power supply voltage supplied by the power supply source, said charging current being used for charging the first capacitive element PA1 a transformer having a primary winding and a secondary winding, PA1 a first branch shunting the first capacitive element and comprising a series arrangement of the primary winding and a switching element, PA1 output terminals coupled to the secondary winding for connecting a load circuit comprising a lamp.
The invention also relates to an illumination unit.
A circuit arrangement as described in the opening paragraph is known from U.S. Pat. No. 4,342,948. The known circuit arrangement is very suitable for generating a voltage having a relatively high amplitude. In practice, it is often found for such a circuit arrangement that the voltage generated by the circuit arrangement has the shape of an attenuated AC voltage because the leakage inductance of the transformer resonates with the first capacitive element. The frequency of the attenuated AC voltage is often relatively high. Since the transport of charge carriers in the ignited lamp is relatively slow, the relatively high frequency of the attenuated AC voltage has the result that the maximum amplitude of the ignition voltage of the lamp is higher than the maximum amplitude of the attenuated AC voltage across the second capacitive element. The ignition behavior of the lamp is thereby influenced positively. A drawback of the relatively high frequency of the attenuated AC voltage is, however, that the ignition voltage is present across the lamp only for a relatively short time. The frequency of the attenuated AC voltage can be modified by modifying the dimensioning of the circuit arrangement. However, the latter would result in a relatively expensive and voluminous circuit arrangement. In practice, the relatively high frequency of the attenuated AC voltage has the result that some lamps do not ignite or only ignite after a relatively large number of attempts.